1. Field of the Invention
The present invention relates to a high-voltage feed-through capacitor and a magnetron using the high-voltage feed-through capacitor.
2. Description of the Related Art
High-voltage feed-through capacitors have been developed to be incorporated into a magnetron as a filter for eliminating unwanted radiation waves generated by oscillation of the magnetron. For example, Japanese Unexamined Patent Application Publication No. 8-078154 discloses a typical construction of such a high-voltage feed-through capacitor.
In the high-voltage feed-through capacitor of this type, since high voltage is to be applied between a grounding metal fitting and a through conductor, it is required to ensure a sufficient withstand voltage between them. In JP 8-078154, for example, a tubular insulating cover is fitted in a recessed portion which is formed on one side of the grounding metal fitting opposite a raised portion, thereby providing a sufficient creeping distance between the grounding metal fitting and the through conductor for insulation.
In the construction disclosed in JP 8-078154, however, the insulating cover, which is adapted to be fitted in the recessed portion of the grounding metal fitting, has a large bottom area. In addition, the tubular insulating cover is so tall as to provide a sufficient creeping distance. Therefore, it is difficult to reduce the external size of the high-voltage feed-through capacitor below the grounding metal fitting.
In the construction disclosed in JP 8-078154, moreover, since the insulating cover is adapted to be fixed to the grounding metal fitting, an insulating resin has to be applied not only to the space inside the capacitor element but also to the space inside the insulating cover. Therefore, the filling amount of the insulating resin necessarily increases, which increases cost and also makes the high-voltage feed-through capacitor susceptible to the thermal expansion/contraction of the insulating resin. Stress caused by the thermal expansion/contraction of the insulating resin may decrease the withstand voltage.